3.1 Overview of photosynthesis


All energy we use originally comes from light energy captured by photosynthesis.

Photosynthetic organisms transform light energy into chemical energy during photosythesis, then use the molecules for respiration.

Other organisms get their energy from consuming these molecules and using them in respiration to produce ATP.

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Site of photosynthesis

The chloroplasts are where photosynthesis takes place.

Adaptations of the leaf for photosynthesis:

  • large surface area - more sunlight.
  • arrangement of leaves to prevent shadowing - more sunlight.
  • thin - short diffusion pathway for gases.
  • transparent cuticle and epidermis - more sunlight.
  • numerous stomata - faster gas exchange.
  • many air spaces in spongy mesophyll - faster gas exchange.
  • xylem and phloem - brings water and takes away sugar.
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structure chloroplast (http://3.bp.blogspot.com/_FLSPZURcXIQ/TIfCswCmXWI/AAAAAAAAANQ/iUlQZBRAc0E/s400/structureofchloroplast.gif)

Grana - Site of light dependent reaction. Stroma - Contains starch. Site of Calvin Cycle.

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Stages of photosynthesis

  • Capturing light energy.
  • Light dependent reaction - The light energy causes an electron flow as it lands on chlorophyll, and photolysis. Products are reduced NADP, ATP and oxygen.
  • Calvin Cycle - The hydrogen ions reduce carbon dioxide to sugars.
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